Anti-microbial activity and inflammation in Hermansky-Pudlak Syndrome type 1

Thesis

Inflammatory bowel disease (IBD) is caused by a breakdown in tolerance of the immune system to the gut microbiota in genetically predisposed individuals. The mechanisms underlying IBD are complex and multifactorial. Monogenic diseases with intestinal inflammation provide important puzzle pieces in identifying key mechanisms of barrier function. Hermansky-Pudlak Syndrome type 1 (HPS-1) features defective vesicle trafficking and can include complications such as Crohn’s-like intestinal inflammation and pulmonary fibrosis. In this thesis, I pinpoint aberrant immunometabolism in HPS-1 patient macrophages using transcriptomics and functional assays. Following bacterial infection, HPS-1 macrophages feature an augmented TNF/OSM signature, which underlies polygenic IBD. I validate the deregulated immunometabolism in HPS1 knockout HAP1 cells, which have defective cholesterol metabolism and enhanced low density lipoprotein uptake. Using lysosomal immunoprecipitation and proteomics, I identify increased mTOR levels on HPS1 knockout lysosomes, which translates into enhanced mTORC1 signaling. The amplified mTORC1 signaling in HPS1 deficiency is mediated by Rab32. The alterations in metabolism and mTORC1 activation cause impaired anti-bacterial immunity in HPS1 knockout cells and HPS-1 patient macrophages. Mass cytometry of HPS-1 peripheral blood reveals an expansion of inflammatory monocytes, while serum proteomics uncovers a TNF/IL-1α signature in HPS- 1. Suppression of mTORC1 signaling through rapamycin treatment rescues the bacterial clearance defect in HPS-1 patient macrophages, providing a novel therapeutic target for HPS- IBD. These findings have implications beyond HPS, since augmented mTOR signaling and derailed metabolism can trigger inflammation in several diseases, such as lysosomal storage disorders.

Authors: Cavounidis, A

• DOI: 10.5287/ora-8j129zv5e
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: Inflammation; Hermansky-Pudlak Syndrome; Monogenic disease; Anti-microbial activity; Inflammatory bowel disease
• Subjects: Immunology; Gastrointestinal system